Why switching to alert through selenium is not stable?

Question

Why switching to alert through selenium is not stable?

For example.
1. Run a code and all good. Everything worked out well. But if this code is run in a few min

Answer 1

This will click the OK button on the alert:

driver.switch_to.alert.accept() 

This will click the CANCEL button on the alert:

driver.switch_to.alert.dismiss()